function parseDateUtc(date: string): Date {
  return new Date(`${date}T00:00:00Z`);
}

function minutesFromTime(time: string): number {
  const [hour, minute] = time.slice(0, 5).split(":").map(Number);
  return hour * 60 + minute;
}

export function computeFractionalDte(date: string, time: string, expiration: string): number {
  const startDay = parseDateUtc(date).getTime();
  const expiryDay = parseDateUtc(expiration).getTime();
  const dayDiff = Math.round((expiryDay - startDay) / 86_400_000);
  const remainingMinutes = Math.max(16 * 60 - minutesFromTime(time), 0);
  return Math.max(dayDiff + remainingMinutes / (24 * 60), 0);
}